Electronic control for the movement of large objects,particularly movable blackboards



FIG.1

w, nu o ss- ETAL 3,525,028 ELECTRONIC CONTROL FOR THE MOVEMENT 0F LARGEOBJECTS PARTICULARLY MOVABLE BLACKBOARDS Filed Aprll 17, 1967 2Sheets-Sheet l INVENTORS= Walter E6105:

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W. RUOSS ET AL ELECTRONIC CONTROL FOR THE MOVEMENT. OF LARGE Aug. 18,1910 OBJECTS, PARTICULARLY MOVABLE BLACKBOARDS Filed April 17. 1967 2Sheets-Sheet 2 w GE INVENTORS S Y MN u. N RE J m (a U N "in W H UnitedStates Patent US. Cl. 318446 1 Claim ABSTRACT OF THE DISCLOSURE Anelectronic control system for large objects which uses linear contactunits instead of spot contacts. The contact unit consists of ahigh-grade insulator carrying two conductors consisting ofnon-oxidizable metal bands and corresponds to the length of the objectto be moved. Contact can be established by bridging the two conductorswith a finger at any desired spot, whereby due to the resistanceinherent in the human skin, but slight current flow is elfected. Thelatter then is amplified and actuates a relay which effects a switchingoperation. The device is particularly useful, but not limited, to theactuation of movable blackboards.

Objects of large dimensions, controlled electrically, such as extensiverotating machines or large vertically movable blackboards, frequentlyrequire electrical contacts for activation or inactivation which must belocated at different points of their frames. These points often areremote from each other.

It is the object of the invention to devise electronic controls for suchlarge objects which has as its salient feature the installation ofcontact means which are not point contacts but linear units. These aredisposed within the area of the object in the form of a strip or barwhich consists of a high-grade insulator carrier whereon twonon-oxidizing metal wires or bands are disposed. When a human finger islaid on any desirable point of the unit, the metal bands areinterconnected. Hence, the current flowing in the contact wires orbands, due to the resistance inherent in the human skin, is very slightbut, by means of a temperature-compensated amplifier, actuates a relaywhich effects a switching operation which ceases upon the removal of thefinger.

The invention will now be further explained with reference to theaccompanying drawings. However, it should be understood that these aregiven merely by way of explanation, and not of limitation, and that itis intended to cover all embodiments of the invention which are withinthe scope and the spirit of the invention as hereinafter claimed.

In the drawings,

FIG. 1 is a perspective of a contact unit;

FIG. 2 is a section through a contact unit;

FIG. 3 is a circuit diagram for a contact unit;

FIG. 4 is a front elevation of a blackboard provided with a contact unitaccording to the invention;

FIG. 5 is a horizontal projection of the blackboard shown in FIG. 4; and

FIG. 6 is an elevation taken along lines II of FIG. 5.

Referring now to these drawings, the contact unit shown in FIGS. 1 and 2consists of a high-grade insulating material 1 as carrier on which twonon-oxidizable metal bars or strips 2, 2a, and two like metal bands 3,3a are disposed. The connecting wires are designated as 5.

FIG. 3 is an electronic circuit diagram wherein a direct current of,e.g., 22 volts is introduced at 6. The slight "ice current flowing, whenfinger '4 touches the contact unit 2, 2a or 3, 3a, is amplifiedapproximately 200 times in transistor 9, and serves to controltransistor 12; the latter controls relay 14 which is provided withhigh-voltage current contacts and controls the motor. Resistance 8 is tolimit the current flow in case of a short circuit in the contact unit.NTC resistances 7 and 10 serve to adapt current and voltage andsimultaneously as temperature compensators. Resistance 11 also serves toadapt current and voltage. The diode 13 protects the switchingtransistor 12. The entire assembly is hooked up to the contact unit bythe connecting wires 5.

While it is evident that the contact unit as described lends itself to amultitude of applications, its utilization on blackboards withvertically movable panels has been found particularly gratifying. Suchblackboards are widely used and frequently have a plurality of panels.To date, the movement of these panels is controlled by motors which areactuated by push button contacts. These are installed in the front or atthe side of the board and actuate a mechanical movement system, i.e.,they operate one of the switches in the system. However, even withblackboards of comparatively small length, a confusing amount of pushbuttons is present from which the lecturer must choose the correct one.With a blackboard of, e.g., 4 m. length, and there are in use todaythose of twice that size, one button each is required for the upward andthe down ward movement and one for stopping. If push button groups wereinstalled at a distance of one meter, five such groups would be requiredand 10 for two panels disposed one behind the other. It follows that thelecturer would have to be concerned with the operation of the blackboardto such an extent that his presentation would suffer therefrom. Hence,the electronic control system according to the invention provides anideal solution.

FIGS. 4-6 illustrate the application of the system according to theinvention to a vertically movable blackboard. These illustrations areschematics and omit the customary accessories, such as motors, etc.

Panel 17 moves between the guide posts 15 and 16. The contact bar 18 hasthe contact units 2, 2a and 3, 3a, and the broken-line (FIG. 4)rectangular oblong denotes the electronic control. The latter isactuated as soon as one of the contact units is touched by a humanfinger at any point. This immediately activates the motor 20, by meansof the electronic control as explained below, and the panel moves asdesired. The current supply is interrupted when the finger is removedfrom the contact bar, and the motor stops so that the panel comes torest in the desired position.

As previously indicated, the circuit is at 6 connected to a directcurrent supply of for instance 22 volts. The resistors 7, 8 and 11 servefor stabilizing the operation of the transistor 9. The resistor 10 isthe working resistor of the transistor 9. The NTC resistors 7 and 10, asindicated, serve to compensate for temperature variations.

The diode 13 eliminates the cutoff voltage peak on the relay 14. Thehigh voltage contacts 22 of the relay 14 serve for closing a switch 19that has contacts 23. The driving motor is indicated 20. A three-phasesystem 21 having a zero conductor forms the power supply for it.

The operation is as follows:

To lower the blackboard 17, the operator will place his finger 4 acrossthe upper rails 2 and 2a. As these rails extend over the entire lengthof the blackboard, the operator does not change his actual position. Byconnecting the two rails with the finger the skin resistance of which isup to 5 megohms, a very small current flows in the transistor 9. Thelatter operates in collector arrangement and therefore causes a currentamplification. This current appears primarily as a base current on theswitching transistor 12 and is suflicient to saturate the transistor 12to such an extent that it becomes so low-resistant in itsemitter-collector circuit that practically the entire supply voltagelies on the relay 14, causing the latter to switch. Across thehigh-voltage contacts 22 of the relay 14 a voltage of for instance 220volts is connected to the coil of the switch 19 which closes thecontacts 23 to energize the motor 20 by connecting it with thethree-phase power supply system 21 that has a voltage of 380 volts. Therotation of the motor may be transferred into a blackboard movement byany known means, for instance a chain drive and a gear (not shown). Bylifting the finger 4 off the rails the current flow and thus themovement of the blackboard are interrupted. For raising the blackboard,the operation just described holds true in identical manner for theparts indexed with b on the reference numerals, the finger 4 being usedto connect the rails 3 and 3a (FIG. 1) and to cause the motor 20 toreverse its sense of rotation. Thus a separate circuit is used for eachdirection of the blackboard.

Any motor may be used in this connection; the embodiment shows analternating current motor of known type. Also the switch 19 may be ofany suitable conventional known type.

The circuit described has the advantage of reacting neither tocapacitive nor to inductive interferences, and operates at extremely lowcurrents.

It should be pointed out that the contact units, contact carriers, i.e.,the entire system, need not be in a straight line but may be in anyshape conforming to the device which it is to serve.

We claim as our invention:

1. A contact unit for the control of the movements of large objectswhich comprises a high-grade insulating carrier; at least twosubstantially parallel non-oxidizing metal strips disposed thereon; alow-voltage power supply connected to said metal strips; said metalstrips being at a distance from each other which can be spanned by ahuman finger for small current flow; means for amplifying said current;and motor and switching means for actuating and stopping said movements;contact between said unit and said motor and switching means beingaccomplishedbylaying a finger across any point of said parallel metalstrips; said low-voltage power supply being of a magnitude as to beinnocuous to the human body and wherein said means for amplifying saidpower supply and said switching and motor means comprise 'a firstamplifying transistor amplifier; a second control transistor connectedin seriestherewith; a diode between said second transistor and oneterminal of said power supply; and a relay between said secondtransistor and the said terminal of said power supply; one resistorconnected at one end thereof to a point between said first and secondtransistors and with the other end thereof connected to said oneterminal of said power supply, and another resistor connected betweensaid first transistor and the other terminal of said power supply.

References Cited UNITED STATES PATENTS 2,576,929 12/1951 Ercolino200-159 X 2,946,956 7/1960 Bradley 3281 3,020,528 2/1962 Swanson et a1.340-235 3,056,907 10/1962 Costanzo 317-149 3,207,905 9/1965 Bray 2502063,218,530 11/1965 Momberg et al. 3l8--478 X 3,255,380 6/1966 Atkins eta1 307-116 X ORIS L. RADER, Primary Examiner A. G. COLLINS, AssistantExaminer

